Adhesives based on rubber

adhesives are obtained from natural (NR) and synthetic rubbers of almost all types:

However, adhesives in which rubbers are introduced to increase the elasticity and viscosity of compositions, as well as stabilizers, for example, dispersion adhesives, do not belong to this group of adhesives.

Rubber-based adhesives are characterized by high elastic characteristics after curing, as a result of which they are widely used for bonding elastic materials. Most often, rubber adhesives ARE CLASSIFIED BY THE TYPE OF RUBBER they contain.

For example, an adhesive based on nitrile rubber is called "nitrile rubber adhesive".

Sometimes they are subdivided into GENERAL and SPECIAL PURPOSE adhesives.

DEPENDING ON THE COMPOSITION, adhesives are divided into two groups.

The first group is NON-VULCANIZING RUBBER ADHESIVES. Bonding with such adhesives is achieved by removing the solvent. Previously, these were mainly one-pack systems based on natural rubber, but now they are also available on the basis of synthetic rubbers.

The second group is VULCANIZING ADHESIVES (sometimes they are called self-vulcanizing). These are two-pack or one-pack formulations.

When gluing with two-pack compounds, their vulcanization begins after mixing the components, one of which is a rubber solution with some additives, the other is a vulcanizing system. Mix the components immediately before applying the adhesive. Their curing (in relation to rubber adhesives, the term vulcanization is often used) can take place both at room temperature and at elevated temperature.

One-pack rubber adhesives can be cured (vulcanized) both at elevated and at room temperature.

Hot vulcanization adhesives are liquid systems (solutions or dispersions) with a viscosity of 0.05-20 Pa*s. They are used both for bonding unvulcanized rubbers with subsequent vulcanization, and for bonding vulcanized rubbers. Hot vulcanizing adhesives typically provide adhesive joints with higher strength and stable performance than cold vulcanizing adhesives. Adhesive joints made with such adhesives have high elasticity, their strength is at the level of rubber strength.

COLD VULCANIZATION adhesives cure in a thin layer. Some types of adhesives, such as those based on silicone rubbers, cure by reacting the curing agent with moisture in the air.

SOLVENTS. In addition to rubbers, most rubber adhesives contain a solvent. From the point of view of technological and operational properties, the best solvents for rubber adhesives are aromatic and chlorine-containing compounds, however, due to toxicity, their use is limited. The most widely used solvents in general purpose adhesives are nefras (predominantly grade C with a boiling point of 80-120°C and a minimum content of aromatic hydrocarbons), ethyl acetate or mixtures thereof.

The most widely used mixtures of ethyl acetate with nefras with a ratio of 2:1 or 1:1 (wt.). To improve the solubility of rubbers, additional toluene or methyl ethyl ketone can be introduced into the composition of these mixtures, ensuring an equal (by weight) content of solvents in such ternary systems. The use of solvent mixtures makes it possible to control the technological properties and ensure the stability of adhesives during their storage and use.

Aliphatic, aromatic and chlorine-containing hydrocarbons and alcohols are also used as solvents for adhesives intended for bonding rubbers for special purposes.

In order to reduce the fire hazard and toxicity of adhesives, they are prepared on the basis of latexes (based on NK, polychloropreon latexes, etc.), the dispersion medium in which is water. Aqueous dispersion adhesives have less tack than similar adhesives with organic solvents.

To increase the strength of adhesive joints, the COMPOSITION of rubber adhesives includes phenol-, urea-, melamine-, alkylphenol-formaldehyde, epoxy, coumarone-indene and adkyd resins, rosin, low molecular weight polystyrene. To maintain high elasticity of adhesives, they are introduced in small amounts of 0.2-10% (wt.).

VULCANIZING AGENTS are selected based on the type of rubber used in the adhesive. For general purpose adhesives, sulfur (0.1-0.3% (wt.)) is most often used in combination with accelerators, metal oxides, combinations of metals with amine-containing compounds, thiourea. Peroxides are widely used in special-purpose adhesives, and the resins used to modify the adhesive are simultaneously vulcanizing agents. In cold vulcanizing adhesives, polyisocyanates, epoxy compounds and amines are used for this purpose. For the vulcanization of organosilicon rubbers, organic peroxides and compounds of a number of oximes are used, it is possible to use tetraethoxy and tetrabutoxysilanes, 2-methoxyethoxysilane and similar products in combination with a catalyst.

PLASTICIZERS for rubber adhesives are mineral oils, lanolin, phthalates, sebacates, esters of aromatic carboxylic acids.

STABILIZERS in rubber adhesives are mainly used to prevent gelation. For this purpose, diethylamine, ethanol and some others are used.

Metal oxides, technical carbon, white soot, aerosil are used as FILLERS. The carbon black is simultaneously used to control the quality of the adhesive mixing.

The strength of adhesive joints depends on the nature of the rubber used in the adhesive and the vulcanizing system. As a rule, the strength of adhesive joints when gluing rubbers is higher than the strength of the rubbers themselves.

WATER-DISPERSION adhesives are usually used for gluing porous materials (paper, leather, fabrics, etc.).

Rubber adhesives are USED in almost all areas of the national economy.

Adhesives based on natural and chloroprene rubbers are most widely used. WHEN GLUING RUBBERS, an adhesive of the same chemical nature as rubber is usually used.

Polyurethane rubber adhesives are capable of bonding rubbers of various chemical nature, which is why they are sometimes called UNIVERSAL rubber adhesives. The properties of adhesives are largely determined by the type of rubber used in their composition.